Weight to Inactivity or Inactivity to Weight?
Although decreased physical activity and increased sedentary time can certainly help promote weight gain in some individuals, findings that we just published in the International Journal of Obesity rather suggest that in kids excess body fat (adiposity) is better at predicting physical inactivity than the other way around. Using a longitudinal study design in a large sample of 8-11 year old Danish children, we observed that their objectively measured (accelerometer) activity levels at the study's outset didn't in fact predict changes in adiposity over the study's 200 day course. In contrast, higher amounts of weight at baseline predicted a decrease in total physical activity and an increase in sedentary time.
Our findings are novel and suggest that adiposity may be a better predictor of physical activity and sedentary behavior changes than the other way around. Of course there's always the possiblity of confounders skewing the results in ours (and any) observational study, but we tried our best to adjust for key variables including age, sex, pubertal status, socioeconomic status and energy density of the diet. One must nevertheless keep in mind that the measurement of behaviors is much more difficult to capture than the measurement of adiposity, implying that the true association between baseline movement behaviors and changes in adiposity may be underestimated.
Although interesting, future studies with longer follow-up periods will be needed to confirm our results. In the meantime, it appears reasonable to suggest that low levels of physical activity and high amounts of sedentary time are more the result of increased body fat than its cause. Our findings can also be relevant to the successful prevention of obesity by changing the focus, so that we must not only think of excess adiposity being the result of poor lifestyle behaviors but also and importantly as poor lifestyle behaviors being the result of excess adiposity.
Assistant Professor in Pediatrics, University of Ottawa
Junior Research Chair in Healthy Active Living and Obesity Research, CHEO Research Institute